Cyclic GMP appears to have an important role in regulating nuclear function and in part its activity is apparently related to alterations in the level of phosphorylation of non-histone chromatin phosphoproteins. In contrast to cyclic AMP studies, nuclear cyclic GMP-dependent protein kinases have not as yet been identified although cytoplasmic cyclic GMP-dependent protein kinases and nuclear cyclic GMP-binding proteins have been shown in many tissues. Cytoplasmic cyclic GMP-dependent protein kinase requires a protein, protein kinase modulator, in order to respond to cyclic GMP. Therefore without the modulator this kinase appears to be cyclic nucleotide-independent as do many of the protein kinases studied in nuclei. The objective of this study is to better characterize the regulatory roles of cyclic GMP and cyclic AMP in the phosphoryation of non-histone chromatin phosphoproteins. With the use of protein kinase modulator, specific protein kinases in nuclei which are regulated by cyclic GMP will be identified, purified and characterized. These enzymes will be clearly distinguished from other nuclear and cytoplasmic nucleotide-dependent and nucleotide-independent protein kinases through the use of controlled isolation procedures and by electrophoretic studies of the patterns of phosphorylation of the non-histone chromatin phosphoproteins by the various kinases. Changes in the affinity of the non-histone chromatin phosphoproteins for DNA and changes in their activity in RNA synthesis will be examined following their phosphorylation by the nuclear cyclic GMP-dependent and nuclear cyclic AMP-dependent and nucleotide independent protein kinases in the absence and presence of substances which differentially alter the substrate specificity and total activity of the individual protein kinases. Differences in the properties of the non-histone proteins following these procedures will give further information about the regulatory roles of cyclic GMP and cyclic AMP in nuclear function.